1. Field of the Invention
The present invention relates to the process of preparing polymeric petroleum resins. It may prove the most advantageous in preparing paint materials, compositions intended for application as insulating coatings, and in the production of plastics and rubber compositions.
Though synthesis of resins from the crude oil is well-known in the art for a comparatively long time and has wide application in chemical industry, the problem of developing a low-cost technology providing for a high yield of highquality polymeric resins has kept its urgency up to now.
2. Description of the Prior Art
Numerous attempts to solve this problem have been heretofore made by selecting polymerization initiators and process conditions but success achieved in one direction (e.g. an increase in the yield of the end product) was accompanied, as a rule, by deterioration of other process variables and resin properties (e.g. a decrease in solubility, an increase in brittleness etc.). In particular, there are known methods of preparing petroleum resins providing for thermal or catalytic initiation of polymerization.
Another process of preparing resins from petroleum products by polymerization of pyrolyzates of unsaturated hydrocarbons when heating (thermal initiation) proceeds at a low speed and is characterized by a comparatively low yield of the end product (see e.g. V. S. Aliev, N. B. Altman "Sinteticheskie smoly iz neftyanogo syrya", "Khimiya" Publishers, M., 1965, p. 89). To speed up the polymerization under thermal initiation, an increase in temperature up to 250.degree. to 280.degree. C. is needed which leads to sharp deterioration in quality of the resin obtained, i.e. molecular weight decreases, resinifying occurs resulting in dark resins due to the presence in the final product of dimers, trimers, codimers, cotrimers, cyclodienes and aryl alkenes, all being hard to separate. Resins thus obtained have a strong and unpleasant smell. For this reason only the process of thermal polymerization of the styrene-containing fraction (boiling point of 140.degree. to 200.degree. C.) of liquid pyrolyzates has commercial application though this application is rather limited. In practicing this process the yield of resin does not exceed 6%, calculated as starting liquid pyrolyzates, and polystyrene resins obtained are characterized by an increased brittleness, do not dissolve in a nontoxic solvent (white spirit) and need to be plastified.
Also known is a process of polymerization of liquid pyrolyzates, using initiators. In accordance with this process, when polymerizing narrow and wide alkenyl aromatic fractions boiling away at a temperature above 100.degree. C., organic peroxides are used as an initiator (see R. G. Ismailov, G. M. Mamedaliev, S. M. Aliev "Issledovanie sostava i prevrashchenia produktov vysokotemperaturnogo raspada uglevodorodov nefti", 1968, pp. 302-364).
Application of initiators, as compared with the thermal polymerization, allows the process to be carried out at moderate temperatures (80.degree. to 140.degree. C.), the yield of resins to be increased 1.5 to 2-fold and at the same time the molecular weight of resins to be increased up to 15000 to 30000; it also allows the coloration of resins to be sharply improved. However, the resins thus obtained are characterized by such disadvantages as low solubility in non-toxic aliphatic solvents, increased brittleness, necessity of plastification. Moreover, disability of the oxidative polymerization in thin layers and low compatibility with vegetable oils limit the possibility of application of these resins in the coating industry as a film-forming material.
In polymerization of diene-cyclodiene-containing fractions of pyrolysis the above-described processes make it possible to obtain resins consisting mainly of dimers, trimers, codimers, cotrimers, dienes and cyclodienes, which possess such disadvantages as dark colour, high brittleness, strong and unpleasant smell, disability to dry in coatings.
Due to said disadvantages, these resins have not found application in the coating industry. Catalytic polymerization of unsaturated fractions of liquid pyrolyzates in the presence of a Friedel-Craft catalyst (metal halides and complexes thereof), and hydrogen fluoride, boron trifluoride, hydrochloric acid, phosphoric acid etc. has been studied in detail.
The process of producing petroleum resins by polymerization of alkenyl aromatic or diene-olefine fractions of liquid pyrolyzates have been commercially practiced. The catalytic polymerization of unsaturated fractions of pyrolysis is carried out at relatively high temperatures (20.degree. to 120.degree. C.); the yield of resins is as a rule higher as compared with that in the processes of both the initiated and thermal polymerization procedures, which can be explained by participation in the polymerization reaction of not only alkenyl aromatic and diene monomers but also olefines contained in the raw material.
However, the processes of the catalytic polymerization of fractions of liquid pyrolyzates in the presence of the Friedel-Craft catalysts have many serious disadvantages among which in the first place are the following:
the need of thorough drying the raw material;
corrosion of the equipment;
formation of contaminated waste water which is difficult to purify;
formation of a stable emulsion at the stage of neutralization and washing-up, decomposition of which emulsion is connected with great difficulties;
low quality of the resins obtained: dark colour, unpleasant smell, a very low molecular weight (up to 100), brittleness and poor drying ability of the coatings based on these resins, increased ash-content and acidity, unsatisfactory water and chemical resistance.
Thus, the processes of catalytic polymerization of unsaturated fractions of liquid pyrolyzates are characterized by that the process is complicated and the resins obtained are of a low quality.
Resins obtained by the catalytic polymerization of alkenylaromatic fractions do not dissolve in nontoxic aliphatic solvents as well as in the case of initiated and thermal polymerization processes.
Resins which are soluble in the aliphatic solvents can be prepared from diene-olefine fractions using a more complicated procedure providing either preliminary separation of cyclodienes from the raw material or application of special nitrogen- and oxygen-containing additives to the Friedel-Craft catalyst, these procedures resulting in higher contamination Resins thus obtained contain dimers, trimers, codimers, contrimers which give these resins and coatings based thereupon an unpleasant smell and toxicity. The coatings based on said resins are characterized by an extremely low weather resistance.
It is believed that the most promising is the process for preparing polymeric petroleum resins, which process comprises polymerization of liquid pyrolyzates of petroleum hydrocarbons when heated in the presence of an initiator and subsequent separation of the end product (see USSR Inventor's Certificate No. 138,377, Int.Cl..sup.2 (CO8F 240/00). According to this process, fractions having boiling point of 110.degree. to 190.degree. C. are used as liquid pyrolyzates of petroleum hydrocarbons. In the polymerization process a peroxide compound such as peroxide, hydroperoxide etc., for example cumene hydroperoxide, is used as an initiator. The petroleum resins being formed are copolymers of styrene, methyl styrenes and indene which are the end product. The end product is separated either by settling resins from polymerizate in heptane or in petroleum ester of by distillating nonpolymerized hydrocarbons with superheated water steam.
As compared with the above-described process, this procedure is more preferable because it does not need such temperatures as in thermal initiation; moreover, it is not accompanied by separation of large amounts of wastes as it occurs in the catalytic initiation. However, this process is not free of some essential disadvantages either. In particular, this process may be practiced but with fractions having boiling point of 110.degree. to 190.degree. C., which adversely effects the yield of the end product and the process profitability as a whole. To illustrate and confirm this disadvantage, it is sufficient to make a step-by-step investigation of the process of transforming starting petroleum products into a polymeric resin. The fraction having boiling point of lower than 110.degree. C. is distilled from liquid pyrolyzates of crude oil followed by separation of the fraction having boiling point of 110.degree. to 190.degree. C. from the residue which separation is carried out by vacuum rectification. The yield of said fraction for liquid pyrolyzates of gases is 16 to 18% by weight; the same for liquid pyrolyzates of gasoline is 20 to 22% by weight, and for liquid pyrolyzates of kerosene-gas oil fractions said yield is 18 to 20% by weight. The fraction having boiling point of 110.degree. to 190.degree. C. contains 25 to 35% by weight of styrene and methyl styrenes, 20 to 35% by weight of indene and methyl indene, 30 to 50% by weight of (C.sub.8 -C.sub.9) aromatic hydrocarbons. Dienes and cyclodienes are absent in said fraction. The yield of the petroleum resins is 20 to 30% by weight for the 110.degree. to 190.degree. C fraction, and 4 to 6.2% by weight for starting liquid pyrolyzates. The resins obtained by this process are characterized by an increased molecular weight (15000 to 40000), an increased softening point (130.degree. to 140.degree. C.), brittleness, low adhesion to various surfaces, low impact strength, unsatisfactory bending strength of coatings. These resins dissolve in toxic aromatic solvents or in mixtures containing aliphatic solvents. They do not dissolve in pure nontoxic aliphatic solvents. The resins obtained by the above described process cannot participate, like condensed vegetable oils do, in oxidative polymerization in thin layer; moreover, they are not compatible with condensed vegetable oils. Limited application of such resins in the composition of paint materials becomes possible after carrying out preliminary plastification with expensive plasticizers (dibutyl phthalate, chlorinated paraffin etc.). The above disadvantages are due to the monomeric composition of the raw material and to the application of only organic peroxides as an initiator. This results in obtaining an aryl alkene resin concentrated with styrene.
It is also important to note that the reaction mixture must be held for 70 to 120 hours during the polymerization process. Naturally, such a duration of the holding exerts an essentially limiting effect upon the output and makes the equipment used in practicing the process more complicated. Attempts to improve the above described procedure by increasing the temperature of the reaction mixture have not led to the desired results because a comparatively slight increase in reaction rate has demanded for an excessively high specific energy consumption. In addition, this procedure involves substantial complication of the processing equipment, a decrease in quality and in the yield of polymeric resins. Said factors in total raise doubts as to economic expediency of solving the existing contradiction by a simple change of the process conditions. The limited character of the source of raw materials (the possibility of using only fractions having boiling point of 110.degree. to 190.degree. C.) should be also attributed to the same totality of factors.
An object of the invention is an essential increase in reaction rate without a considerable increase in temperature by expanding the range of starting materials, and changing the polymerization initiator thus reducing the price of the process and that of the end product.